Optical system with cant indication

ABSTRACT

An electronic indicator on a see-through optical scope indicates whether an optical system is canted. The indicator may include illuminable visual indicators positioned on opposite sides of a field of view through the optical scope. The indicator may be visual, haptic, or aural. The visual indicator may include one or more LEDs positioned on the periphery of the field of view, and may be optically coupled to an appropriate position on the face of the reticle using a suitable waveguide. The LEDs are coupled to a microprocessor which is, in turn, coupled to a solid-state electronic inclinometer that is incorporated into the internal structure of the optical system. The microprocessor is configured to selectively illuminate one or more of the visual indicators based on the output of the inclinometer, thereby indicating how the reticle is canted, if at all.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. non-provisional patentapplication Ser. No. 16/688,965, filed Nov. 19, 2019, titled “OPTICALSYSTEM WITH CANT INDICATION,” which is a continuation of U.S.non-provisional patent application Ser. No. 15/220,254, filed Jul. 26,2016, titled OPTICAL SYSTEM WITH CANT INDICATION, which claims benefitfrom U.S. provisional patent application No. 62/197,187, filed Jul. 27,2015, titled OPTICAL SYSTEM WITH CANT INDICATION, the contents of all ofwhich are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This disclosure relates generally to gun sighting systems, and morespecifically, to gun sighting systems that are capable of indicatingwhether the sighting system is canted off-center.

BACKGROUND

Accuracy and precision are of critical importance in a wide range ofballistics applications, examples of which include target shooting,hunting, self-defense, military, and law enforcement applications.Because the uncertainty associated with the unaided aiming of a firearmor other weapon is often significant, many improvements have been madeto increase a shooter's ability to accurately hit an intended target.One such improvement is a telescopic sight, which is also sometimesreferred to as a riflescope, or more simply, a scope, which areoftentimes mounted on long guns, but may also be used in conjunctionwith some handguns. A scope provides improved viewing of the target, forexample using optical magnification, and therefore helps the shootervisualize where a projectile will go. In addition to providingmagnification, a scope will also often include a reticle having stadiamarks or other visual indicia that can be used to facilitaterange-finding and to help the shooter adjust for the gravitational andaerodynamic (crosswind) forces that affect the trajectory of aprojectile. For example, many reticles provide multiple aiming pointsfor aiming at different distances or under different wind conditions.

Although a properly mounted and calibrated scope will help a shootercompensate for gravitational and aerodynamic forces, the way the firearmis held can still adversely affect the accuracy of the shot. Inparticular, side-to-side tilt of a scope mounted to a firearm, alsoreferred to as “cant”, is a potentially significant source ofinaccuracy, and therefore even if a shooter makes appropriateadjustments for range and windage, his/her shot may still miss itsintended target if the scope is canted even slightly off-center. FIGS.1A and 1B illustrate cant. FIG. 1A illustrates a long gun having anoptical system 10, such as a scope, mounted thereon. The optical system10 has a long axis 12, which may also be referred to as the optical axisor the z axis. FIG. 1B illustrates the view directly along the z axis ofthe optical system 10, and illustrates two other axes. These axesinclude a horizontal transverse axis 14, and a vertical transverse axis16. The transverse axes 14, 16 are both transverse to the z axis.Vertical deflection, or cant, of a system may be measured as deflectionof the optical system from the vertical transverse axis 16. For example,an instantaneous axis 18 is not aligned with the vertical transverseaxis 16. The mis-alignment between the instantaneous axis 18 and thevertical transverse axis 16 is caused by rotation about the z axis. Thisrotation amount, also referred to as cant or cant angle, is illustratedin FIG. 1B as the angle ⊖ 20.

Canting a firearm to a small or even imperceptible degree can result insignificant error downrange, particularly as the distance to the targetincreases. In a typically mounted scope, the optical axis of the scopeis approximately one or two inches above the bore of the firearm. Inthis case, when the firearm and the scope are canted off-center, thebore of the firearm moves in the opposite direction as the scope. Theresulting error manifests as both a horizontal and vertical deflectionfrom the intended target. This error is illustrated in FIG. 2 , which isa graph indicating projectile deflection at various ranges as a functionof firearm cant angle. The data illustrated in FIG. 2 were modeled basedon the trajectory of a 30 caliber, 180 grain Nosler ballistic tiphunting bullet fired from a .300 Winchester Magnum cartridge. At 1500yards, only 1° of firearm cant results in 20.92 inches (1.74 feet) ofhorizontal deflection. Canting the firearm 10° results in 12.24 inches(at 500 yards), 65.28 inches (at 1000 yards), or 208.17 inches (at 1500yards) of horizontal deflection. Vertical deflection is lesser inmagnitude than horizontal deflection, but is still significant enough tomake an otherwise accurate shot miss its target.

The data illustrated in FIG. 2 demonstrates the importance of reducingor eliminating cant when sighting a target through a scope. Inparticular, it should be appreciated that even if the shooter's intendedtarget is properly sighted in the scope, a slight—and possiblyimperceptible—cant may result in an errant shot. Many shooters rely onan inner sense of balance to ensure that their firearm is not canted.However, this reliance presupposes that the shooter has a fullyfunctional, unimpaired sense of balance that reliably translates intothe ability to hold a firearm without any cant. This often turns out notto be the case, particularly for shooters who are exposed todisorienting influences such as loud sounds and strong forces associatedwith shooting a firearm; repeated focusing on distant targets as viewedthrough one eye; prolonged periods of standing; exposure to theelements; and traversing or standing upon uneven, canted, and/or slopedterrain.

A number of systems have been developed to supplement a shooter's senseof balance and detect a canted firearm. For example, bubble- and/orfluid-based levels have been adapted for mounting on a firearm, scope,or mounting ring. These systems have limited precision due to fluidviscosity, are subject to freezing in extreme cold, are difficult to seein low light conditions, and often require the shooter to divert his/herattention from the target to determine whether the firearm is canted.For example, mechanical bubble levels are often installed on theexterior body of the riflescope or on an upper portion of a scope ringmount, thus requiring the shooter to move his/her eye away from thesight to see the bubble level. U.S. Pat. No. 6,978,569 discloses variousembodiments of a firearm tilt indicator that relies on a physicalmechanism, such as a gravity pendulum or a rolling ball. Mechanicalsystems such as these also often have limited precision, and they tendto fall out of calibration or otherwise fail after repeatedly beingsubjected to recoil forces. These shortcomings represent substantialobstacles to the development of a robust and reliable cant detectionsystem that does not distract the shooter's attention from the target,and that can be used in a wide range of tactical environments. Othersystems that display scope cant are also known, such as gun scope havinga full Heads Up Display (HUD), as described in US Patent publication2014/0184476. Such HUDs act as an opaque screen on which targetinginformation may be displayed. Other versions may overlay HUD informationaround the periphery of an optical viewing area. HUDs are generallyfragile, expensive, and suffer negatively from exposure to rain, coldand other wet conditions that are often encountered in a typical huntingenvironment.

Embodiments of the invention address these and other limitations of theprior art.

SUMMARY

One embodiment is directed to a direct, see-through optical systemhaving a main optical axis extending from an ocular end to an objectiveend of the optical system. The main optical axis of the optical systemis structured to be fixedly aligned with a long axis of a shootingdevice. The see-through optical system includes an electronicinclinometer structured to determine a cant of the shooting devicerelative to a vertical transverse axis of the main optical axis of theoptical system, and also includes an electronic indicator structured toprovide an indicator signal to a user related to the determined cant.

In one aspect of the invention, the electronic indicator is a lightsystem including a first indicator for clockwise cant and a secondindicator for counter-clockwise cant. The electronic indicator mayinclude a third indicator for indicating a vertical alignment of theshooting device with the optical system. The optical system may behoused in a telescopic sighting device having a front focal plane and arear focal plane, and the first or second indicator may be locatedproximate the front focal plane, the second plane, or an eyepiece of thetelescopic sighting device. In some embodiments the first or secondindicator is located on a field stop proximate the rear focal plane. Insome embodiments the electronic indicators are located near an outsideedge of a viewing area of the optical system. In some embodiments thefirst and second indicator may be located on opposite sides of theoptical system.

In some embodiments the electronic indicator may include a plurality ofindividual indicators, and may be disposed in an arc located near anoutside edge of the viewing area of the optical system.

In some embodiments the electronic indicator is structured to indicate adirection of cant and a relative amount of cant such as, for example, byindicating the amount of cant by a flashing rate or increasing lightintensity of the electronic indicator.

In some embodiments the electronic indicator is structured to indicate avertical alignment of the shooting device with the optical system byilluminating both the first and second indicator.

In some embodiments the electronic indicator may be a haptic indicatoror an aural indicator.

In some embodiments the electronic inclinometer is an accelerometer.

Other embodiments include an optical sighting system having a mainoptical axis structured to align with a gun barrel when mounted to agun, which includes a rotation detector structured to measure an amountof rotation of the gun barrel about its long axis, a plurality ofelectronic light indicators structured to provide one or more lightsignals to a user indicative of the measured amount and direction ofrotation of the gun barrel, and an electronic controller coupled to therotation detector and structured to cause the plurality of lightindicators to generate the one or more light signals.

In some aspects the electronic controller may include an electronicinclinometer, such as an accelerometer, structured to measure aninstantaneous amount of gun barrel rotation about is long axis.

In some embodiments the electronic controller is coupled to a usercontrollable switch, which may be used to control a light intensity ofthe one or more light signals.

Yet other embodiments are directed to a cant-detecting reticle assemblyincluding a reticle having a horizontal axis that includes a targetpoint, a first cant indicator position on a first side of the targetpoint, and a second cant indicator position on a second side of thetarget point that is opposite the first side, a first light emitteroptically coupled to the first cant indicator position, such that whenthe first light emitter is activated, the first cant indicator positionis illuminated, a second light emitter optically coupled to the secondcant indicator position, such that when the second light emitter isactivated, the second cant indicator position is illuminated, aninclinometer configured to generate a first signal in response todetecting that the reticle is canted in a first direction, and a secondsignal in response to detecting that the reticle is canted in a seconddirection that is opposite the first direction, and a controller that isconfigured to activate the first light emitter in response to receivingthe first signal from the inclinometer, and to activate the second lightemitter in response to receiving the second signal form theinclinometer.

In some embodiments the first and second cant indicator positions arelocated at opposite ends of the horizontal axis.

In some embodiments the cant-detecting reticle assembly further includesa printed circuit board to which the inclinometer and the controller aremounted.

In some embodiments the cant-detecting reticle assembly further includesa flexible circuit, wherein the flexible circuit supports conductorsextending from the controller to the first and second light emitters.

In some embodiments the cant-detecting reticle assembly further includesa ring-shaped reticle holder disposed in a first focal plane, whereinthe reticle is mounted in an interior portion of the reticle holder, andthe first and second light emitters are positioned on an exteriorcircumferential surface of the reticle holder. In other embodiments thefirst and second light emitters are positioned other than on the reticleor reticle holder.

In some embodiments the cant-detecting reticle assembly further includesa third light emitter optically coupled to the target point, such thatwhen the third light emitter is activated, the target point isilluminated, and the controller is further configured to activate thethird light emitter steadily when neither of the first and secondsignals are received from the inclinometer.

In other embodiments a third light emitter is optically coupled to thetarget point, such that when the third light emitter is activated, thetarget point is illuminated and the controller is further configured toactivate the third light emitter intermittently when either of the firstand second signals are received from the inclinometer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an example riflescope illustrating along axis.

FIG. 1B is a graph illustrating orientation of various axes relative tothe long axis illustrated in FIG. 1A.

FIG. 2 is a graph indicating projectile deflection at various ranges asa function of firearm cant angle.

FIG. 3 is a perspective view of an example riflescope that may be usedwith a reticle that is capable of indicating whether the riflescope iscanted off-center.

FIG. 4 schematically illustrates the frontward appearance of an examplereticle that is capable of indicating whether an optical system iscanted off-center.

FIG. 5 schematically illustrates the rearward appearance of an examplereticle that is capable of indicating whether an optical system iscanted off-center.

FIG. 6A schematically illustrates the frontward appearance of an examplereticle that is capable of indicating whether an optical system iscanted off-center, wherein the reticle is mounted in a ring-shapedreticle holder.

FIG. 6B schematically illustrates the reticle and reticle holderassembly of FIG. 6A, as viewed along line 6B-6B.

FIG. 7 schematically illustrates a cross-sectional view of an exampletechnique for coupling light from a peripherally-positioned lightemitter to an aperture formed in a reticle.

FIG. 8 schematically illustrates the configuration of an exampleflexible circuit that can be used in conjunction with the reticleillustrated in FIG. 4 .

FIG. 9 schematically illustrates selected components included within anauxiliary turret of the riflescope illustrated in FIG. 3 , the selectedcomponents supporting the operation of a reticle that is capable ofindicating whether the riflescope is canted off-center.

FIG. 10 is a circuit diagram illustrating selected electronic componentsthat can be used to control the operation of an example reticle that iscapable of indicating whether an optical system is canted off-center.

FIG. 11A illustrates the appearance of the reticle illustrated in FIG. 4when the reticle is viewed through an optical sighting device that iscanted counterclockwise (CCW).

FIG. 11B illustrates the appearance of the reticle illustrated in FIG. 4when the reticle is viewed through an optical sighting device that iscanted clockwise (CW).

FIG. 11C illustrates the appearance of the reticle illustrated in FIG. 4when the reticle is viewed through an optical sighting device that isnot canted.

DETAILED DESCRIPTION

The various embodiments of an optical system having cant detection andindication disclosed herein are, compared to previous devices, lesssusceptible to error caused by exposure to adverse environmentalconditions and/or recoil forces. They also tend to reduce or eliminatethe need for the shooter to divert his/her attention from a sightedtarget to check a cant indicator, and the illuminated indicators workwell in low light conditions. They are more rugged and less fragile thanHUD systems. They can also be retrofitted to existing scopes. These andother advantages will be apparent from the following disclosure.

The various embodiments disclosed herein are described in conjunctionwith a projectile aiming system that is configured for use with a rifleand that is embodied in the type of telescopic sight typically referredto as a riflescope. However, such embodiments may also be implementedwith projectile aiming systems other than riflescopes, including systemssuch as reflex sights, bow sights, pistol sights and digital sights.Such systems may be used on weapons other than rifles, including deviceswhich are capable of propelling projectiles along substantiallypre-determinable initial trajectories. Examples of such devices includehandguns, pistols, shotguns, bows, crossbows, artillery, trebuchets, andthe like.

Furthermore, while several of the embodiments disclosed herein aredescribed in conjunction with a shooter attempting to hit an intendedtarget, it will be appreciated that such embodiments can also be used toaccurately mount a riflescope to a firearm. For example, in oneimplementation a firearm is fixed in a level position, for example usinga vice or other temporary fixed holder. The firearm includes mountingrings that are used to support a riflescope. The riflescope is placed inthe mounting rings. The user sights through the riflescope and ensuresthat the scope is not canted before tightening the mounting rings andfixing the relatively alignment of riflescope and firearm. Such atechnique is significantly more likely to result in a substantiallyaligned system as compared to a manual alignment, particularly since animperceptible degree cant may result in significant error downrange.

FIG. 3 is a perspective view of a riflescope 100 that may be used withan indicator system that is capable of indicating whether riflescope 100is canted off-center. The indicator is positioned within riflescope 100,along its optical axis, and therefore is generally not visible in theexterior perspective view illustrated in FIG. 3 , but in otherembodiments the indicator may be visible to the exterior of theriflescope. An objective end 110 of riflescope 100 is positioned towardthe intended target, while an ocular end 120 is positioned adjacent tothe shooter's eye. Riflescope 100 includes an elevation turret 140 whichcan be used to adjust the vertical calibration of the reticle, and awindage turret 150 which can be used to adjust the horizontalcalibration of the reticle. An auxiliary turret 160 can be used toprovide other adjustments or manipulations to riflescope 100, such as aparallax compensation adjustment or, for implementations that include anilluminated reticle, an illumination brightness control 162. The reticleis preferably aligned with the riflescope turrets, for example to within±3° or ±1°. While auxiliary turret 160 is positioned on the side of theriflescope body in the illustrated embodiment, in other embodiments itmay be placed on the top of the riflescope body adjacent to ocular end120.

In the illustrated embodiment, riflescope 100 includes electronics thatrely on a power source, and therefore includes a battery that isaccessible via a removable cover 164 that forms part of auxiliary turret160. In one embodiment removable cover 164 is threaded onto the body ofauxiliary turret 160, while in other embodiments a snap-fitconfiguration is used. In still other embodiments auxiliary turret 160is omitted altogether and its associated functionality, such as reticleillumination control, is optionally incorporated into one or more of theother turrets. Riflescope 100 also optionally includes a magnificationcontrol 170 and/or a focus control 180. While many implementations aredescribed in the context of riflescope 100, other embodiments can beimplemented in conjunction with a wide range of different telescopicsighting systems, and thus it will be appreciated that the particularcombination and arrangement of features illustrated in FIG. 3 may bemodified in other embodiments.

In some embodiments the cant indicator may be integrated into or on areticle. A reticle is an object or image that is viewable through theeyepiece of an optical sighting device. Example reticles include strandsof hair, spider web silk, synthetic fibers, wires, electroformedmetallic elements, or any other sufficiently thin and strong material. Areticle helps the shooter aim the fire arm toward a target. While avirtually unlimited range of different reticle shapes and configurationsexist, perhaps the simplest reticle design is a crosshair formed byperpendicularly intersecting lines in the same of a plus symbol (+).Other common reticle configurations include dots, posts, circles,scales, or any combination of the foregoing, with the particularconfiguration being selected based on the intended use of the devicethat incorporates the reticle. When used in conjunction with projectileaiming systems, reticles often include stadia marks that facilitaterange-finding. For example, a reticle that includes stadia marks can beused to estimate the range to objects of known size and the size ofobjects at known range, thus helping a shooter more accuratelycompensate for factors such as gravitational effects (also referred toas “bullet drop compensation”) and windage. In some applicationsreticles are configured with stadia markings that includes ballistichold-over points that are matched for long-range precision shooting.

FIG. 4 schematically illustrates the frontward appearance of an examplereticle 200 that is capable of indicating whether an optical system iscanted off-center. As used herein, the term “frontward appearance”refers, in addition to its ordinary meaning, to the appearance ofreticle 200 when viewed under normal usage conditions, that is, fromocular end 120 of riflescope 100. From this perspective, the intendedtarget would appear behind reticle 200, that is, in the −z direction asillustrated in FIG. 4 . Reticle 200 includes horizontal and verticalstadia lines that meet at a target point. Depending on the demands of aparticular implementation, the stadia lines may or may not be ofconstant width, and may or may not extend across the entire field ofview. The example embodiment illustrated in FIG. 4 , for instance,includes stadia lines which are wider near the reticle periphery, andwhich are narrower near the target point. In such embodiments, reticle200 is formed using a flattened wire or an electroformed metallicelement, although other materials can be used in other embodiments.

The horizontal stadia line of reticle 200 includes a CCW cant indicatorposition 210 and a CW cant indicator position 220 which are located onopposite sides of the center target point. A level indicator position230 is optionally located at the target point. In the illustratedembodiment, the cant indicators are in the shape of an upward pointingtriangle and the level indicator is in the shape of a circle. However,different shapes can be used for these indicators in other embodiments.The indicators provide a path for light to pass through reticle 200 atthe respective indicator positions, thus giving the indicator anilluminated appearance, as will be described in turn. In particular,light generated by a CCW LED 214 is visible at CCW cant indicatorposition 210, light generated by a CW LED 224 is visible at CW cantindicator position 220, and light generated by a center LED 234 isvisible at level indicator position 230. These LEDs are positionedaround the periphery of reticle 200, and are connected to a controller240 via a flexible circuit 250.

A wide range of alternative configurations may be implemented. Forexample, while FIG. 4 illustrates the CCW and CW cant indicatorpositions as being located on opposite sides of the target point, inother embodiments the cant indicator positions may be positionedelsewhere in the field of view, including both on one side of the targetpoint. In some cases one or more of the cant indicator positions may belocated above or below the horizontal stadia line. While LEDs are usedas a light sources in the illustrated embodiment, other light sourcescan be used in other embodiments. While position 230 is referred to as alevel indicator position, it will be appreciated that in embodimentswherein such position is continuously illuminated regardless of whetheror not the system is canted, such position may also be referred to as atarget indicator, an aiming point indicator, or another similar term.

FIG. 5 schematically illustrates the rearward appearance of reticle 200.As used herein, the term “rearward appearance” refers, in addition toits ordinary meaning, to the appearance of reticle 200 when viewed fromthe opposite (+z) direction as in FIG. 3 , and therefore the rearwardappearance would not be visible under normal use of riflescope 100. Ascan be seen from this perspective, reticle 200 includes a CCW lightguide 216 positioned to propagate light emitted from CCW LED 214 throughCCW cant indicator position 210 such that the light is visible fromocular end 120 of riflescope 100. Reticle 200 also includes a CW lightguide 226 positioned to propagate light emitted from CW LED 224 throughCW cant indicator position 220 such that the light is visible fromocular end 120 of riflescope 100. Likewise, reticle 200 includes acenter light guide 236 positioned to propagate light emitted from centerLED 234 such that the light is visible from ocular end 120 of riflescope100. Center light guide 236 is longer than the other light guidesbecause it extends to the target point at the center of reticle 200.

The light guides illustrated in FIG. 5 may include any suitable materialcapable of propagating visible light, examples of which include fiberoptic cables, as well as plastic, polymeric, or glass waveguides. Forexample, in one embodiment an optical fiber has one end cut at a 450angle to the optical axis of the fiber, thus forming a reflectivesurface that causes the light emitted by the peripheral LEDs to beredirected along the optical axis toward ocular end 120 of riflescope100 (+z direction). This allows the user to look directly at the lightemitter through the optical fiber. In such embodiments the light emittedby the peripheral LEDs is not reflected off electroformed reticlematerial. In such embodiments the optical fiber can be mounted to thefront or rear of reticle 200. Mounting the optical fiber to the front ofreticle 200 tends to be easier to manufacture, but may introduceparallax since the fiber is on a different focal plane than the actualelectroformed reticle. Alternatively, mounting the optical fiber to therear of reticle 200 and aligning the reflective surface with a smallaperture in the electroformed reticle allows the reticle and the lightsource to be substantially coplanar, thus reducing eliminating parallax.

In an alternative embodiment a light-propagating channel is etched intoreticle 200. In another alternative embodiment the light guides areomitted altogether, and light emitted from the peripheral LEDsilluminates reflective electroformed reticle materials deposited at theindicator positions illustrated in FIG. 4 . Additional details withrespect to how light is coupled and propagated amongst the variouscomponents illustrated in FIG. 5 will be described in turn. Because thelight guides are formed on and/or positioned behind the reticle stadiawires, they are generally not visible to a user not looking throughriflescope 100. FIG. 5 also illustrates that the aforementioned LEDs arepositioned around the periphery of reticle 200, and are connected tocontroller 240 via flexible circuit 250.

FIG. 6A schematically illustrates the frontward appearance of reticle200 having been mounted in a ring-shaped reticle holder 260. Reticleholder 260 is used to secure and mount reticle 200 within the body ofriflescope 100, and thus these components are configured to fit securelytogether for example using a snap fit and/or an epoxy. Reticle holder260 is also used to secure flexible circuit 250 and the LEDs mountedthereto. This is made clear with reference to FIG. 6B, whichschematically illustrates the assembly of FIG. 6A, as viewed along line6B-6B, that is, in the xz plane. In particular, FIG. 6B illustratesreticle 200 positioned within reticle holder 260. Flexible circuit 250is positioned around an exterior circumferential surface of reticleholder 260. The light sources CCW LED 214, CW LED 224, and center LED234 are mounted to flexible circuit 250 at appropriate locations aroundthe circumference of reticle holder 260. In particular, FIG. 6Billustrates that center LED 234 is positioned at the bottom-center ofreticle holder 260, while CCW LED 214 and CW LED 224 are positioned atthe left and right sides, respectively, of reticle holder 260.

FIG. 7 schematically illustrates a cross-sectional view of an exampletechnique for coupling light from a peripherally-positioned lightemitter to an aperture formed in reticle 200. More specifically, FIG. 7illustrates reticle 200 mounted in reticle holder 260. Reticle 200includes CCW cant indicator position 210, which can be seen as formingan aperture in reticle 200, thereby allowing the reticle and the lightsource to be positioned in the same focal plane, thus reducing oreliminating parallax. Flexible circuit 250 is positioned on an exteriorcircumferential surface of reticle holder 260, and supports CCW LED 214,which is mounted thereto. Reticle holder 260 further includes a holderaperture 262 configured to allow light emitted by CCW LED 214 to passthrough reticle holder 260 and enter CCW light guide 216. In certainembodiments holder aperture 262 is filled with a light transmittingmaterial, for example the same material that comprises CCW light guide216, while in other embodiments, such as that illustrated in FIG. 7 ,holder aperture 262 is empty space. CCW light guide 216 includes areflective surface 228 that is angled so as to reflect light that isemitted from CCW LED 214, and that is transmitted via CCW light guide216, through CCW cant indicator position 210. Such light is then visibleto a user looking through riflescope 100 in the direction of theintended target (the −z direction). In one embodiment, reflectivesurface 228 includes reflective electroformed reticle material. WhileFIG. 7 illustrates the transmission of light from CCW LED 214 throughCCW cant indicator position 210, it will be appreciated that a similarconfiguration can be used to transmit light (a) from CW LED 224 throughCW cant indicator position 220, and (b) from center LED 234 throughlevel indicator position 230.

The example embodiment illustrated in FIGS. 6A, 6B, and 7 illustrate CCWcant indicator position 210 and CW cant indicator position 220 beingpositioned on a horizontal stadia line of reticle 200, horizontallyoffset from reticle holder 260. In alternative embodiments, however,cant indicator positions 210, 220 are not positioned on the reticleitself, but rather on another element that forms part of the opticalsystem. For example, in one alternative embodiment wherein a glassreticle is mounted in a black or other dark-colored field stop thatfunctions as reticle holder 260, CCW cant indicator position 210 and CWcant indicator position 220 may be formed in the field stop itself, asopposed to being positioned on a stadia line of reticle 200. Thisalternative embodiment reduces the degree to which reticle 200 ismanipulated by coupling thereto components such as light guides 216,226, or forming cant indicator positions 210, 220 therein. Such anembodiment may be particularly useful in conjunction with a front focalplane (FFP) optical system wherein the aiming reticle is positioned onthe first focal plane. This is because a FFP optical system allows thereticle image to magnify as the objective image is magnified. As thereticle image is magnified, the perimeter features of the reticle, suchas indicator positions 210, 220 are no longer visible. In FFP opticalsystems, it may therefore be preferred to locate indicator positions210, 220 in reticle holder 260, field stop, eyepiece, or in anotherlocation that would remain visible and stationary, appearing as acircumferential border or frame to the magnified reticle 200, regardlessof the applied magnification. In any embodiment, the indicator may bepositioned anywhere that the user may view the indicator while lookingthrough the scope, be it at or near the front focal plane, at or nearthe rear focal plane, in or near an eyepiece, or anywhere where theindicator may be used by the shooter.

FIG. 8 schematically illustrates an example configuration of flexiblecircuit 250. As described herein, in certain embodiments flexiblecircuit 250 is positioned along an exterior circumferential surface ofreticle holder 260. In alternative embodiments, flexible circuit 250 canbe integrated into, or otherwise positioned in an interior portion ofreticle holder 260. In still other embodiments, flexible circuit 250 iscoupled directly to reticle 200. Light emitters CCW LED 214, CW LED 224,and center LED 234 are mounted to flexible circuit 250, for exampleusing soldered connections. A plurality of conductors 252 extend fromcontroller 240 to the light emitters. Conductors 252 include a groundconductor and an individual voltage lead dedicated to each emitter,thereby allowing each emitter to be controlled independently of theothers. Conductors 252 are coupled to controller 240 via a plurality ofvoltage leads 254.

FIG. 9 schematically illustrates selected components included withinauxiliary turret 160 of riflescope 100, the selected componentssupporting or otherwise controlling the operation of reticle 200. Forexample, auxiliary turret 160 houses a battery 166 that is accessiblevia removable cover 164, and that functions as a power source for theaforementioned light sources. In one embodiment battery 166 comprises athree-volt coil cell lithium battery, although any of a wide variety ofsuitable power sources can be used in other embodiments. In theillustrated embodiment auxiliary turret 160 also houses a printedcircuit board 168 on which electronics that enable and control operationof reticle 200 are mounted. Such electronics include controller 240 andan inclinometer 270. Mounting these components on printed circuit board168 enables both to share the common power supply provided by battery166.

Controller 240 is electronically connected to the aforementioned lightemitting elements (for example, CCW LED 214, CW LED 224, and center LED234) via conductors 252 which are mounted on flexible circuit 250.Firmware in controller 240 is capable of individually illuminating thevarious light emitters in response to signals received from inclinometer270. In one implementation controller 240 is a Model STM8L151C2U6ultra-low-power microcontroller manufactured by STMicroelectronics(Geneva, Switzerland). Brightness control 162 is coupled to controller240 via printed circuit board 168, thereby further allowing the user tomanipulate the operation of reticle 200. In one embodiment brightnesscontrol 162 comprises a rotatable switch that is coupled to apotentiometer on printed circuit board 168. Other configurations can beimplemented in other embodiments. It will be appreciated that certain ofthe components illustrated in FIG. 9 may be electronically connected toeach other with appropriate connectors and/or conductors which are notillustrated for clarity.

FIG. 10 is a circuit diagram illustrating one particular implementationof selected electronic components that can be used to control the cantindicator. Certain of these components (such as controller 240 andinclinometer 270) may be mounted on printed circuit board 168 itself,while other components (such as battery 166, CCW LED 214, CW LED 224,and center LED 234) may be electronically coupled to printed circuitboard 168 or other components mounted thereto. For instance, the exampleembodiment illustrated in FIG. 10 includes a switch 280 that can be usedto disable the device when not in use, thereby preserving battery life.In such embodiments switch 280 is optionally coupled to a mechanicalswitch positioned on the exterior of riflescope 100, for example onauxiliary turret 160.

Inclinometer 270, which may be embodied by an accelerometer, is asolid-state electronic device configured to determine whether riflescopeis canted off-center. The accelerometer may be a 1-axis, 2-axis, or3-axis accelerometer, for example. In other embodiments the inclinometer270 may be any device capable of detecting and/or measuring cant. In theexample embodiment illustrated in FIG. 9 , inclinometer 270 isvertically oriented (in the yz plane), although it may be calibrated foruse in other orientations as well. Thus, in certain embodimentsinclinometer 270 is calibrated and aligned with reticle 200 duringmanufacture of riflescope 100 to detect rotation around the z-axis,which is the optical axis of riflescope 100. In other embodiments thecant indicator is separate from the reticle 200, but still aligned withthe optical axis of the riflescope 100. Calibration may additionally oralternatively be performed when riflescope 100 is mounted to a firearm.In one implementation inclinometer 270 is a Model LIS2DH12ultra-low-power, high-performance, three-axis inclinometer manufacturedby STMicroelectronics (Geneva, Switzerland). Any of a variety of othersuitable inclinometers can be used in alternative embodiments. Theoutput signals generated by inclinometer 270 are provided to controller240 via circuitry mounted on printed circuit board 168.

For example, if inclinometer 270 detects that riflescope 100 is cantedCCW around the optical axis (the z-axis), controller 240 can beconfigured to illuminate CCW LED 214 steadily. Alternatively, ifinclinometer 270 detects that riflescope 100 is canted CW around theoptical axis (z-axis), controller 240 can be configured to illuminate CWLED 224 steadily. In either case, controller 240 can also be configuredto illuminate center LED 234 intermittently, such as in a blinkingfashion. These reticle configurations, which are illustrated in FIG. 11A(CCW cant) and FIG. 11B (CW cant), provides the shooter with a quickindication that riflescope 100 is not level, even without requiring theshooter to divert his/her attention from the center target point of thereticle. In particular, even without perceiving either of theilluminated cant indicator positions at the periphery of reticle,blinking level indicator position 230 at the center target point conveysto the shooter that the riflescope is canted. The steady illumination ofone of the cant indicator positions conveys to the shooter how to adjusthis/her hold on the firearm (for example, by rotation) to obtain a levelshot. Likewise, if the shooter sees that level indicator position 230 issteadily illuminated, he/she will understand that the riflescope is notcanted, again without diverting attention from the central target point.This reticle configuration is illustrated in FIG. 11C. This designavoids distracting the shooter with many lights or other potentialdistractions when he/she is ready to discharge the firearm.

In alternative embodiments reticle 200 can be configured to indicate thepresence of cant using other combinations of illuminated cantindicators. For example, in an embodiment wherein the optional centrallevel indicator position 230 is omitted, CCW LED 214 or CW LED 224 canbe configured to illuminate, optionally intermittently (in a blinkingfashion), depending on how the riflescope 100 is canted, if at all. Insuch embodiments the rate at which an illuminated cant indicator blinksis optionally proportional to the degree of cant, for example such thatmore extreme cant angles result in more rapid blinking of the indicator.As the reticle is rotated to achieve a level position the blinkingslows, with the cant indicators eventually turning off completely whenriflescope 100 is not canted. The absence of any illuminated cantindicators within the riflescope 100 indicates that the riflescope isheld level. The use of variably-blinking cant indicators can also beused in another alternative embodiment wherein the central target pointis always illuminated, which may be useful when implemented inconjunction with an illuminated reticle. In general, the use ofvariable-blinking cant indicators with a steadily illuminated (oraltogether omitted) target point may be particularly useful inconjunction with riflescopes which are occasionally used at short rangeswhere a slight cant is less critical and the blinking target point couldbe distracting. Other combinations of illuminated cant indicators, andoptionally a central target point indicator, can be used in otherembodiments.

Although the above discussion described in detail how the cantindicators may be integrated into or associated with the reticle 200 ofthe riflescope 100, embodiments of the invention are not limited toalways being mounted on or adjacent to the reticle 200. A riflescope 100may be generally described as a direct-view, see-through, or opticalscope. Such scopes are made from a transparent material, most commonlyglass or plastic, and allow a direct viewing of a target when a userlooks through the ocular end 120 of the riflescope 100. Each riflescope100 includes a front focal plane and a rear focal plane, which are bothin focus to the user's eyes when the riflescope is properly focused.Operation of the magnification control 170 causes indications on thefront focal plane, if any, to appear larger or smaller through theriflescope 100 depending on which way the magnification control isoperated. Embodiments of the invention may include indicators that arephysically located on either of the front of the front or rear focalplane. Carrying a light signal to the front focal plane may includeusing a longer flexible circuit 250 than illustrated in FIG. 6B, or byusing longer light guides, such as the CCW light guide 216 illustratedin FIG. 7 . In this manner the indicator signal may be physicallylocated anywhere within the field of view through the riflescope 100 asthe user is looking through the riflescope.

In yet other embodiments the cant indicator need not be a visualindicator, but may instead (or in addition to) include a haptic or anaural indicator. With reference to FIGS. 9 and 10 , in such systems onlyminor modifications to the LED driving circuit need be made. For thehaptic indicator embodiment, the Center, CCW and CW LEDs 214, 234, 224may be replaced by or operated in conjunction with a haptic generator,such as a vibratory motor. A switch may be placed in a position thatallows the user to operate it while the user is simultaneously lookingthrough the riflescope 100. For example, the switch may be located nearthe trigger of the firearm, or further down the barrel in a positionwhere the switch may be operated by the hand used to support thefirearm. When the switch is depressed, the inclinometer 270 andcontroller 240 operate as described above, detecting the rotation aboutthe z-axis of the firearm. A haptic signal is then generated in responseto the switch press. Particular haptic patterns may indicate variousamounts or directions of rotation. For example, a short vibration mayindicate CW rotation, two short vibrations may indicate CCW rotation,and a long vibration may indicate that the riflescope 100 is verticallyaligned. A similar system may be used with the cant indicator generatingan aural feedback. In an example aural system, a short chirp of apiezo-electric speaker may indicate CW rotation, a two chirp signalindicates CCW rotation, and a long chirp indicates that the riflescope100 is vertically aligned. In some embodiments any or all of thesefeedback systems may be employed, either in conjunction or independentlyoperated. A selector switch or programmable setting (not illustrated)allows the user to select which and how many indicator systems, visual,haptic, or aural, will be used.

The foregoing detailed description has been presented for the purposesof illustration and description. It is not intended to be exhaustive orto limit the invention to the particular disclosed embodiments. Numerousvariations and configurations will be apparent in light of thisdisclosure. Thus its intended that the scope of the invention be definednot be this detailed description, but rather by the claims appendedhereto.

1. A direct, see-through optical system having a main optical axisextending from an ocular end to an objective end of the optical system,the main optical axis of the optical system structured to be fixedlyaligned with a long axis of a shooting device, the see-through opticalsystem comprising: an electronic inclinometer structured to determine acant of the shooting device relative to a vertical transverse axis ofthe main optical axis of the optical system; an aiming reticle in theoptical system visible to a user when viewing along the main opticalaxis; and an electronic indicator structured to provide an indicatorsignal at or near a center portion of the reticle to a user related tothe relative amount of cant.
 2. The see-through optical system of claim1, in which the relative amount of cant is indicated by a flashing rateof the electronic indicator.
 3. The see-through optical system of claim1, in which the relative amount of cant is indicated by a lightintensity of the electronic indicator.
 4. The see-through optical systemaccording to claim 1, in which the electronic indicator flashes when therelative amount of cant is beyond a threshold amount of relative cant.5. The see-through optical system according to claim 1, in which theelectronic indicator does not flash when the relative amount of cant isbelow a threshold amount of relative cant.
 6. The see-through opticalsystem according to claim 5, in which the electronic indicator isintegrated into the reticle.
 7. The see-through optical system accordingto claim 1, in which the electronic indicator comprises a Light EmittingDiode (LED).
 8. The see-through optical system according to claim 7, inwhich the electronic indicator further comprises a light propagatingmaterial.